diff --git a/src/Spout/Writer/AbstractWriter.php b/src/Spout/Writer/AbstractWriter.php
index 68d452f..80438c1 100644
--- a/src/Spout/Writer/AbstractWriter.php
+++ b/src/Spout/Writer/AbstractWriter.php
@@ -69,17 +69,18 @@ abstract class AbstractWriter implements WriterInterface
      * By using this method, the data will be written to a file.
      *
      * @param  string $outputFilePath Path of the output file that will contain the data
+     * @param string $sheetName The custom name of the sheet
      * @return \Box\Spout\Writer\AbstractWriter
      * @throws \Box\Spout\Common\Exception\IOException If the writer cannot be opened or if the given path is not writable
      */
-    public function openToFile($outputFilePath)
+    public function openToFile($outputFilePath, $sheetName = null)
     {
         $this->outputFilePath = $outputFilePath;
 
         $this->filePointer = $this->globalFunctionsHelper->fopen($this->outputFilePath, 'wb+');
         $this->throwIfFilePointerIsNotAvailable();
 
-        $this->openWriter();
+        $this->openWriter($sheetName);
         $this->isWriterOpened = true;
 
         return $this;
@@ -204,5 +205,4 @@ abstract class AbstractWriter implements WriterInterface
         $this->closeWriter();
         $this->isWriterOpened = false;
     }
-}
-
+}
\ No newline at end of file
diff --git a/src/Spout/Writer/Helper/XLSX/FileSystemHelper.php b/src/Spout/Writer/Helper/XLSX/FileSystemHelper.php
index fddbb25..daaa0dd 100644
--- a/src/Spout/Writer/Helper/XLSX/FileSystemHelper.php
+++ b/src/Spout/Writer/Helper/XLSX/FileSystemHelper.php
@@ -249,10 +249,13 @@ EOD;
     <Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.sheet.main+xml" PartName="/xl/workbook.xml"/>
 
 EOD;
+    
+    $escaper = new \Box\Spout\Common\Escaper\XLSX();
 
     /** @var Worksheet $worksheet */
     foreach ($worksheets as $worksheet) {
-        $contentTypesXmlFileContents .= '    <Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.worksheet+xml" PartName="/xl/worksheets/sheet' . $worksheet->getId() . '.xml"/>' . PHP_EOL;
+        $worksheetName = $worksheet->getExternalSheet()->getName();
+        $contentTypesXmlFileContents .= '    <Override ContentType="application/vnd.openxmlformats-officedocument.spreadsheetml.worksheet+xml" PartName="/xl/worksheets/' . $escaper->escape(strtolower($worksheetName)) . '.xml"/>' . PHP_EOL;
     }
 
     $contentTypesXmlFileContents .= <<<EOD
@@ -288,7 +291,7 @@ EOD;
         foreach ($worksheets as $worksheet) {
             $worksheetName = $worksheet->getExternalSheet()->getName();
             $worksheetId = $worksheet->getId();
-            $workbookXmlFileContents .= '        <sheet name="' . $escaper->escape($worksheetName) . '" sheetId="' . $worksheetId . '" r:id="rIdSheet' . $worksheetId . '"/>' . PHP_EOL;
+            $workbookXmlFileContents .= '        <sheet name="' . $escaper->escape($worksheetName) . '" sheetId="' . $worksheetId . '" r:id="rId' . $worksheetId . '"/>' . PHP_EOL;
         }
 
         $workbookXmlFileContents .= <<<EOD
@@ -316,10 +319,13 @@ EOD;
 
 EOD;
 
+        $escaper = new \Box\Spout\Common\Escaper\XLSX();
+
         /** @var Worksheet $worksheet */
         foreach ($worksheets as $worksheet) {
+            $worksheetName = $worksheet->getExternalSheet()->getName();
             $worksheetId = $worksheet->getId();
-            $workbookRelsXmlFileContents .= '    <Relationship Id="rIdSheet' . $worksheetId . '" Target="worksheets/sheet' . $worksheetId . '.xml" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/worksheet"/>' . PHP_EOL;
+            $workbookRelsXmlFileContents .= '    <Relationship Id="rId' . $worksheetId . '" Target="worksheets/' . $escaper->escape(strtolower($worksheetName)) . '.xml" Type="http://schemas.openxmlformats.org/officeDocument/2006/relationships/worksheet"/>' . PHP_EOL;
         }
 
         $workbookRelsXmlFileContents .= '</Relationships>';
diff --git a/src/Spout/Writer/Internal/XLSX/Workbook.php b/src/Spout/Writer/Internal/XLSX/Workbook.php
index e6ca0db..060fbf8 100644
--- a/src/Spout/Writer/Internal/XLSX/Workbook.php
+++ b/src/Spout/Writer/Internal/XLSX/Workbook.php
@@ -62,13 +62,18 @@ class Workbook
     /**
      * Creates a new sheet in the workbook. The current sheet remains unchanged.
      *
+     * @param string $sheetName The custom name of the sheet
      * @return Worksheet The created sheet
      * @throws \Box\Spout\Common\Exception\IOException If unable to open the sheet for writing
      */
-    public function addNewSheet()
+    public function addNewSheet($sheetName = null)
     {
         $newSheetNumber = count($this->worksheets);
         $sheet = new Sheet($newSheetNumber);
+        if( !empty($sheetName) )
+        {
+            $sheet->setName($sheetName);
+        }
 
         $worksheetFilesFolder = $this->fileSystemHelper->getXlWorksheetsFolder();
         $worksheet = new Worksheet($sheet, $worksheetFilesFolder, $this->sharedStringsHelper, $this->shouldUseInlineStrings);
@@ -132,7 +137,7 @@ class Workbook
      * @param Worksheet $worksheet
      * @return void
      */
-    protected function setCurrentWorksheet($worksheet)
+    public function setCurrentWorksheet($worksheet)
     {
         $this->currentWorksheet = $worksheet;
     }
diff --git a/src/Spout/Writer/Sheet.php b/src/Spout/Writer/Sheet.php
index fd86c18..d2a27d5 100644
--- a/src/Spout/Writer/Sheet.php
+++ b/src/Spout/Writer/Sheet.php
@@ -27,6 +27,16 @@ class Sheet
         $this->name = self::DEFAULT_SHEET_NAME_PREFIX . ($sheetNumber + 1);
     }
 
+    /**
+     * @param string $sheetName The custom name of the sheet
+     * @return void
+     */ 
+    public function setName($sheetName)
+    {
+        $sheetName = str_replace(' ', '_', $sheetName);
+        $this->name = $sheetName;
+    }
+    
     /**
      * @return int Number of the sheet, based on order of creation (zero-based)
      */
diff --git a/src/Spout/Writer/XLSX.php b/src/Spout/Writer/XLSX.php
index 62e98f1..874ef06 100644
--- a/src/Spout/Writer/XLSX.php
+++ b/src/Spout/Writer/XLSX.php
@@ -66,15 +66,24 @@ class XLSX extends AbstractWriter
     /**
      * Configures the write and sets the current sheet pointer to a new sheet.
      *
+     * @param string $sheetName The custom name of the sheet
      * @return void
      * @throws \Box\Spout\Common\Exception\IOException If unable to open the file for writing
      */
-    protected function openWriter()
+    protected function openWriter($sheetName = null)
     {
         if (!$this->book) {
             $tempFolder = ($this->tempFolder) ? : sys_get_temp_dir();
             $this->book = new Workbook($tempFolder, $this->shouldUseInlineStrings, $this->shouldCreateNewSheetsAutomatically);
-            $this->book->addNewSheetAndMakeItCurrent();
+            if( empty($sheetName) )
+            {
+                $this->book->addNewSheetAndMakeItCurrent();
+            }
+            else
+            {
+                $worksheet = $this->book->addNewSheet($sheetName);
+                $this->book->setCurrentWorksheet($worksheet);
+            }
         }
     }
 
@@ -125,6 +134,18 @@ class XLSX extends AbstractWriter
         return $this->book->getCurrentWorksheet()->getExternalSheet();
     }
 
+    /**
+     * Returns the the workbook for the XLSX file
+     *
+     * @return Book The workbook for the XLSX file
+     * @throws \Box\Spout\Writer\Exception\WriterNotOpenedException If the writer has not been opened yet
+     */
+    public function getBook()
+    {
+        $this->throwIfBookIsNotAvailable();
+        return $this->book;
+    }
+    
     /**
      * Sets the given sheet as the current one. New data will be written to this sheet.
      * The writing will resume where it stopped (i.e. data won't be truncated).